Like most performers, puppeteers will often have a promotional kit that can give you an idea of what they have to offer. The standard promo kit includes photos, brochures, testimonials, and sometimes even video of a past performance.
Skilled puppeteers may not be as easy to come by as clowns, magicians, or other artists. You may have to call one in from outside your local area, which may add a travel fee to the amount you're already paying for the performance. It should not, however, be exorbitant.